A screen design method for printing single crystal PERC cells

Abstract

The invention discloses a screen design method for printing single crystal PERC cells, comprising the following steps: S1: designing the thickness of the screen gauze and the thickness of the PI film, and then designing several silicon wafers with different screen opening widths according to the thickness of the screen gauze and the thickness of the PI film; S2: measuring the width of the printed grid line, the height of the printed grid line, and calculating the aspect ratio; S3: measuring the broken grid ratio of the screen-printed grid line cell under the opening width according to the screen opening width; S4: on the premise that the broken grid ratio is less than 0.08%, screening out data combinations with smaller width of the printed grid line and larger aspect ratio; S5: according to the data combinations screened out in S4, using different data combinations to print screen front electrodes and grid lines on the silicon wafer; S6: performing a single-piece silver paste consumption experiment and a cell electrical performance parameter experiment on the screen printed by using the different data combinations screened out in S4, and comparing with the data of the conventional screen, obtaining the group of data with the best performance.

Description

Technical Field

[0001] The invention relates to a screen design method for printing single crystal PERC cells. Background Art

[0002] With the advent of the era of grid parity, reducing production costs and improving the photoelectric conversion efficiency of solar cells have become one of the main methods to improve the competitiveness of the photovoltaic industry. At present, single-crystal PERC (passivated emitter rear contact) solar cells are the mainstream products of crystalline silicon solar cells. The front electrode grid line is an important component of single-crystal PERC solar cells. It is responsible for collecting and transmitting the photocurrent generated by the solar cell, and has a vital impact on the photoelectric conversion efficiency of single-crystal PERC solar cells. Screen printing has become the mainstream process method for the production of industrial single-crystal PERC cell electrodes due to its mature process, high efficiency and low cost.

[0003] Initially, the single crystal SE bifacial PERC cell used an emulsion screen with screen parameters of 430-13 (430 mesh, 13 wire diameter). However, the emulsion screen had poor printing accuracy, small aspect ratio of the secondary grid line, low screen life, and was prone to blockage, causing problems such as false printing and broken grid, thus affecting the quality and electrical performance of the cell. With the improvement of screen technology, the use of non-photosensitive material polyimide (PI film) instead of the emulsion coating on the screen surface has improved the wear resistance and service life of the screen, while improving the printing accuracy and reducing the broken grid ratio. In order to further improve efficiency and reduce costs, the positive electrode grid line of crystalline silicon solar cells is developing towards refinement, complexity, and high aspect ratio, and the screen is also developing towards high mesh and ultra-fine wire diameter. The emergence of 520-11 (520 mesh, 11 wire diameter) PI film screen has ushered in a new era of ultra-fine grid line printing technology, realizing the printing of ultra-fine grid lines (below 30μm), reducing the shading area, and improving the aspect ratio of the secondary grid lines. However, there are few studies on how to match mesh parameters and PI film thickness in 520-11 PI film screen. The present invention designs a matching experiment of different mesh parameters and PI film thickness parameters for 520-11 PI film screen, and deeply studies the influence of different matching methods on the unit watt cost and electrical performance of solar cells. Summary of the invention

[0004] The purpose of the present invention is to solve the above-mentioned deficiencies in the prior art and to provide a screen design method for printing single crystal PERC cells.

[0005] A screen design method for printing a single crystal PERC cell comprises the following steps:

[0006] S1: The thickness of the screen gauze is designed to be a, and the thickness of the PI film is designed to be b. Then, according to the thickness a of the screen gauze and the thickness b of the PI film, several silicon wafers with different screen opening widths are designed. The screen opening widths of the above silicon wafers are c1, c2, ... c n ;

[0007] S2: According to the screen opening width c n , measure the width of the printed grid line as d n , the height of the printed grid line is h n , and calculate the aspect ratio

[0008] S3: According to the screen opening width c n , measure the broken grid ratio s of the screen-printed grid cell under the opening width n ;

[0009] S4: The ratio of broken gate s n <0.08% as the premise, screen out the width d of the printed grid line n Smaller, aspect ratio n Larger data sets;

[0010] S5: Based on the data combinations selected in S4, the silicon wafers that have undergone texturing, diffusion, laser re-doping, PSG removal, alkaline polishing, PECVD back-side deposition of Al2O3 / SiNx stacked passivation film, PECVD front-side deposition of SiNx anti-reflection film, laser grooving and back-field printing are used to print the screen front electrodes and grid lines using different data combinations;

[0011] S6: Conduct single-chip silver paste consumption experiment and battery cell electrical performance parameter experiment on the screen printed with different data combinations screened out in S4, and compare with the data of conventional screen to obtain the set of data with the best performance.

[0012] As a further improvement, the thickness of the screen mesh is designed to be 17μm, the thickness of the PI film is 8μm, the screen opening widths are 16μm, 17μm and 18μm respectively, the widths of the printed grid lines corresponding to the screen opening widths are 27.41μm, 28μm and 29.33μm respectively, the heights of the printed grid lines are 9.358μm, 9.278μm and 9.302μm respectively, the aspect ratios are 34.14%, 33.16% and 31.72% respectively, and the broken grid ratios of the battery cells are 0.09%, 0.04% and 0.02% respectively.

[0013] As a further improvement, under the premise of ensuring printability, that is, the broken grid ratio is less than 0.08%, the line width is as narrow as possible and the aspect ratio is as high as possible to ensure higher conversion efficiency. When the mesh thickness is 17μm and the PI film thickness is 8μm, the most matching screen opening width is 17μm.

[0014] As a further improvement, the thickness of the screen mesh is designed to be 17μm, the thickness of the PI film is 10μm, the screen opening widths are 17μm, 18μm and 19μm respectively, the widths of the printed grid lines corresponding to the screen opening widths are 28.91μm, 29.86μm and 30.87μm respectively, the heights of the printed grid lines are 11.24μm, 11.12μm and 11.09μm respectively, the aspect ratios are 38.88%, 37.24% and 35.92% respectively, and the broken grid ratios of the battery cells are 0.12%, 0.07% and 0.03% respectively.

[0015] As a further improvement, under the premise of ensuring printability, that is, the broken grid ratio is less than 0.08%, the line width is as narrow as possible and the aspect ratio is as high as possible to ensure higher conversion efficiency. When the mesh thickness is 17μm and the PI film thickness is 10μm, the most matching screen opening width is 18μm.

[0016] As a further improvement, the thickness of the screen mesh is designed to be 19μm, the thickness of the PI film is 10μm, the screen opening widths are 18μm, 19μm and 20μm respectively, the widths of the printed grid lines corresponding to the screen opening widths are 30.39μm, 31.63μm and 33.18μm respectively, the heights of the printed grid lines are 12.05μm, 12.07μm and 11.94μm respectively, the aspect ratios are 39.65%, 38.16% and 35.99% respectively, and the broken grid ratios of the battery cells are 0.15%, 0.11% and 0.06% respectively.

[0017] As a further improvement, under the premise of ensuring printability, that is, the broken grid ratio is less than 0.08%, the line width is as narrow as possible and the aspect ratio is as high as possible to ensure higher conversion efficiency. When the mesh thickness is 19μm and the PI film thickness is 10μm, the most matching screen opening width is 20μm.

[0018] As a further improvement, the conventional screen mesh number is 430 meshes, the wire diameter is 13 μm, the mesh thickness is 20 μm, the PI film thickness is 8 μm, the opening width is 20 μm, the width of the printed grid line is 34.91 μm, the height is 11.88 μm, and the aspect ratio is 34.03%.

[0019] Beneficial effects:

[0020] The present invention utilizes a 520-mesh, 11-wire-diameter polyimide film (PI film) knotless screen, designs experiments on matching different mesh parameters with PI film thickness parameters, and determines different usage effects achieved by matching different mesh parameters with PI film thickness parameters, thereby achieving the goal of minimizing the production cost of battery cells and maximizing the conversion efficiency of battery cells. DETAILED DESCRIPTION

[0021] In order to deepen the understanding of the present invention, the present invention will be further described in detail below in conjunction with examples. The examples are only used to explain the present invention and do not constitute a limitation on the protection scope of the present invention.

[0022] Example 1

[0023] A method for matching the thickness of a positive electrode screen gauze and a PI film with low silver consumption, wherein the gauze thickness is 17 μm, the PI film thickness is 8 μm, and the screen opening width is 17 μm. The conventional screen mesh number is 430 meshes, the wire diameter is 13 μm, the gauze thickness is 20 μm, the PI film thickness is 8 μm, and the opening width is 20 μm.

[0024] The cell obtained by screen printing the front grid line electrode described in Example 1 is compared with the cell obtained by conventional screen printing the front grid line electrode. The change in the silver paste consumption of the printed front grid line electrode is shown in Table 1, and the change in the electrical performance of the cell is shown in Table 2. It can be seen from Table 1 that compared with the conventional screen, the silver paste consumption of the single piece of Example 1 is significantly reduced. Compared with the conventional screen, the silver paste consumption of the single piece of Example 1 is reduced by 12.6 mg in the sample experiment, 15.9 mg in the small batch experiment, and 18 mg in the medium batch experiment.

[0025] It can be seen from Table 2.1, Table 2.2 and Table 2.3 that compared with the traditional screen, the electrical performance of the cell in Example 1 has declined. Compared with the traditional screen, the open circuit voltage of the cell in Example 1 has no significant change, the short circuit current has been significantly improved, and the filling factor has decreased. This is because the open circuit voltage of the battery is jointly determined by the recombination rate of the PN junction and the surface. The increase in the width of the gate line will not affect the PN junction, but will directly affect the surface recombination rate. There are many defect energy levels in the energy band of the metal and silicon metallization area. The existence of these defect energy levels will act as a recombination center, resulting in an increase in the recombination current, thereby affecting the open circuit voltage. However, the change in the width of the grid line of Example 1 and the conventional screen is less than 5μm, which will not have a significant effect on the voltage; the width of the screen-printed grid line in Example 1 is narrow, the shading area at the emitter of the battery is reduced, the number of photogenerated carriers is increased, and the short circuit current is increased, but the lower grid line width will affect the contact and increase the contact resistance of the grid line of the cell, thereby reducing the filling factor FF. The increase in the short circuit current is lower than the loss value of the filling factor, making the final photoelectric conversion efficiency of Example 1 low. Compared with the traditional screen, the conversion efficiency of Example 1 in the sample experiment was reduced by 0.06%, the conversion efficiency of Example 1 in the small batch experiment was reduced by 0.06%, and the conversion efficiency of Example 1 in the medium batch experiment was reduced by 0.5%.

[0026] Table 1 Changes in silver paste consumption of front grid lines in Example 1 compared with conventional screens

[0027]

[0028] Table 2.1 Battery electrical performance parameters in Example 1 compared with conventional screens in sample experiments

[0029]

[0030] Table 2.2 Small batch experiment example 1 compared with conventional screen plate battery electrical performance parameters

[0031]

[0032] Table 2.3 Batch Experiment Example 1 Compared with Conventional Screen Solar Cell Electrical Performance Parameters

[0033]

[0034] Example 2

[0035] A method for matching the thickness of the positive electrode screen gauze and PI film with comprehensive efficiency and silver medal consumption, wherein the gauze thickness is 17μm, the PI film thickness is 10μm, and the screen opening width is 18μm. The conventional screen mesh number is 430 mesh, the wire diameter is 13μm, the gauze thickness is 20μm, the PI film thickness is 8μm, and the opening width is 20μm.

[0036] The cell obtained by screen printing the front grid line electrode described in Example 2 is compared with the cell obtained by conventional screen printing the front grid line electrode. The change in the silver paste consumption of the printed front grid line electrode is shown in Table 3, and the improvement in the electrical performance of the cell is shown in Table 4. It can be seen from Table 3 that compared with the conventional screen, the silver paste consumption of the single piece of Example 2 is reduced. Compared with the conventional screen, the silver paste consumption of the single piece of Example 2 is reduced by 6.4 mg in the sample experiment, 10.1 mg in the small batch experiment, and 11.21 mg in the medium batch experiment.

[0037] It can be seen from Table 4.1, Table 4.2 and Table 4.3 that the electrical performance of the battery cell is basically the same as that of the traditional screen in Example 2. Compared with the traditional screen, there is no obvious change in the open circuit voltage of Example 2 in the sample experiment, the short circuit current is improved, and the fill factor is slightly reduced. Because the screen-printed grid line width of Example 2 is widened, the shading area at the battery emitter is increased, the number of photogenerated carriers is reduced, and the short circuit current is reduced, but the grid line height is increased, resulting in an increase in the grid line aspect ratio, which improves the FF and ultimately improves the conversion efficiency of the battery cell. Compared with the traditional screen, the conversion efficiency of the battery cell in Example 2 in the sample experiment is improved by 0.03%; the conversion efficiency of the battery cell in the small batch experiment is improved by 0.02%; the conversion efficiency of the battery cell in the medium batch experiment is improved by 0.01%.

[0038] Table 3 Changes in silver paste consumption of front grid lines in Example 1 compared with conventional screens

[0039]

[0040] Table 4.1 Battery electrical performance parameters in Example 1 compared with conventional screens in sample experiments

[0041]

[0042] Table 4.2 Small batch experiment example 1 compared with conventional screen plate battery electrical performance parameters

[0043]

[0044] Table 4.3 Batch Experiment Example 1 Compared with Conventional Screen Solar Cell Electrical Performance Parameters

[0045]

[0046] Example 3

[0047] A method for matching the thickness of a positive electrode screen gauze and a PI film with high conversion efficiency, wherein the thickness of the screen gauze is 19 μm, the thickness of the PI film is 10 μm, and the screen opening width is 20 μm. The conventional screen mesh number is 430 meshes, the wire diameter is 13 μm, the screen gauze thickness is 20 μm, the PI film thickness is 8 μm, and the opening width is 20 μm.

[0048] The cell obtained by screen printing the front grid line electrode described in Example 3 is compared with the cell obtained by conventional screen printing the front grid line electrode. The change in the silver paste consumption of the printed front grid line electrode is shown in Table 5, and the improvement in the electrical performance of the cell is shown in Table 6. It can be seen from Table 5 that compared with the conventional screen printing, the silver paste consumption of the single piece in Example 3 is slightly reduced. In the sample experiment, the silver paste consumption of the single piece is reduced by 1.1 mg, in the small batch experiment, the silver paste consumption of the single piece is reduced by 3.9 mg, and in the medium batch experiment, the silver paste consumption of the single piece is reduced by 4.3 mg.

[0049] It can be seen from Table 6.1, Table 6.2 and Table 6.3 that compared with the traditional screen, the electrical performance of the battery cell in Example 3 is significantly improved. Compared with the conventional screen, the open circuit voltage and fill factor of the battery cell in Example 3 do not change significantly, and the short-circuit current is improved. Because the printed grid lines in Example 3 are narrower than those printed on the conventional screen, the shading area is smaller, the number of photogenerated carriers increases accordingly, and it has a higher aspect ratio, which reduces the contact resistance of the grid lines of the battery cell, thereby increasing the fill factor FF, and ultimately significantly improving the photoelectric conversion efficiency of the battery cell. Compared with the conventional screen, the conversion efficiency of Example 3 increased by 0.09% in the sample experiment, the conversion efficiency increased by 0.8% in the small batch experiment, and the conversion efficiency increased by 0.8% in the medium batch experiment.

[0050] Table 5 Changes in silver paste consumption of front grid lines in Example 1 compared with conventional screens

[0051]

[0052] Table 6.1 Battery cell electrical performance parameters compared with conventional screen in Example 1 in sample experiment

[0053]

[0054] Table 6.2 Small batch experiment example 1 compared with conventional screen plate battery electrical performance parameters

[0055]

[0056] Table 6.3 Batch Experiment Example 1 Compared with Conventional Screen Cell Electrical Performance Parameters

[0057]

[0058] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A screen design method for printing single crystal PERC cells, characterized in that: The following steps are involved: S1: The thickness of the screen gauze is designed to be a, and the thickness of the PI film is designed to be b. Then, according to the thickness a of the screen gauze and the thickness b of the PI film, several silicon wafers with different screen opening widths are designed. The screen opening widths of the above silicon wafers are c1, c2, ..., c n ; S2: According to the screen opening width c n , measure the width of the printed grid line as d n , the height of the printed grid line is h n , and calculate the aspect ratio S3: According to the screen opening width c n , measure the broken grid ratio s of the screen-printed grid cell under the opening width n ; S4: The ratio of broken gate s n <0.08% as the premise, the width d of the printed grid line is screened n Smaller, aspect ratio n Larger data sets; S5: Based on the data combinations selected in S4, the silicon wafers that have undergone texturing, diffusion, laser re-doping, PSG removal, alkaline polishing, PECVD back-side deposition of Al2O3 / SiNx stacked passivation film, PECVD front-side deposition of SiNx anti-reflection film, laser grooving and back-field printing are used to print the screen front electrodes and grid lines using different data combinations; S6: Conduct single-chip silver paste consumption experiment and battery cell electrical performance parameter experiment on the screen printed with different data combinations screened out in S4, and compare with the data of conventional screen to obtain the set of data with the best performance.

2. A screen design method for single crystal PERC battery printing according to claim 1, characterized in that: The designed thickness of the screen mesh is 17μm, the thickness of the PI film is 8μm, the screen opening widths are 16μm, 17μm, and 18μm, respectively. The widths of the printed grid lines corresponding to the screen opening widths are 27.41μm, 28μm, and 29.33μm, respectively. The heights of the printed grid lines are 9.358μm, 9.278μm, and 9.302μm, and the aspect ratios are 34.14%, 33.16%, and 31.72%, respectively. The broken grid ratios of the battery cells are 0.09%, 0.04%, and 0.02%, respectively.

3. A screen design method for single crystal PERC battery printing according to claim 2, characterized in that: Under the premise of ensuring printability, that is, the broken grid ratio is less than 0.08%, the line width is as narrow as possible and the aspect ratio is as high as possible to ensure higher conversion efficiency. When the mesh thickness is 17μm and the PI film thickness is 8μm, the most matching screen opening width is 17μm.

4. A screen design method for single crystal PERC battery printing according to claim 1, characterized in that: The designed screen mesh thickness is 17μm, the PI film thickness is 10μm, the screen opening widths are 17μm, 18μm, and 19μm, respectively. The widths of the printed grid lines corresponding to the screen opening widths are 28.91μm, 29.86μm, and 30.87μm, respectively. The heights of the printed grid lines are 11.24μm, 11.12μm, and 11.09μm, and the aspect ratios are 38.88%, 37.24%, and 35.92%, respectively. The broken grid ratios of the battery cells are 0.12%, 0.07%, and 0.03%, respectively.

5. A screen design method for single crystal PERC battery printing according to claim 4, characterized in that: Under the premise of ensuring printability, that is, the broken grid ratio is less than 0.08%, the line width is as narrow as possible and the aspect ratio is as high as possible to ensure higher conversion efficiency. When the mesh thickness is 17μm and the PI film thickness is 10μm, the most matching screen opening width is 18μm.

6. A screen design method for monocrystalline PERC cell printing according to claim 1, characterized in that: The designed thickness of the screen mesh is 19μm, the thickness of the PI film is 10μm, the screen opening widths are 18μm, 19μm, and 20μm, respectively. The widths of the printed grid lines corresponding to the screen opening widths are 30.39μm, 31.63μm, and 33.18μm, respectively. The heights of the printed grid lines are 12.05μm, 12.07μm, and 11.94μm, and the aspect ratios are 39.65%, 38.16%, and 35.99%, respectively. The broken grid ratios of the battery cells are 0.15%, 0.11%, and 0.06%, respectively.

7. A screen design method for single crystal PERC battery printing according to claim 6, characterized in that: Under the premise of ensuring printability, that is, the broken grid ratio is less than 0.08%, the line width is as narrow as possible and the aspect ratio is as high as possible to ensure higher conversion efficiency. When the mesh thickness is 19μm and the PI film thickness is 10μm, the most matching screen opening width is 20μm.

8. The screen design method for monocrystalline PERC cell printing according to claim 1, characterized in that: The conventional screen mesh number is 430 mesh, the wire diameter is 13μm, the mesh thickness is 20μm, the PI film thickness is 8μm, the opening width is 20μm, the width of the printed grid line is 34.91μm, the height is 11.88μm, and the aspect ratio is 34.03%.

Images